This invention relates to electrical fuel cells.
The applicant has applied for a patent with Application Number PCT/AU97/00488 for a FUEL CELL AND A PROCESS OF USING A FUEL CELL under the Patent Cooperation Treaty. The patent was published on Feb. 12, 1998 with Publication Number WO 98/06145.
The above fuel cell consisted of a separate anode cell and a separate cathode cell with two electrodes in each cell adjacent to each other. Fuel is fed into the anode cell and oxidant is fed into the cathode cell. Ions produced in one cell are transported to the other cell to provide the ion transfer for the fuel cell reactions. The electronic circuit is completed through the load, the connection of the one electrode in the anode cell to another electrode in the cathode cell by an external conductor, and through the electrolyte between the adjacent electrodes at the anode cell and at the cathode cell.
This fuel cell eliminated the diffusion of ions through a media common to prevailing conventional fuel cells such as the proton electrolytic membrane fuel cell, the molten carbonate fuel cell, and the solid oxide fuel cell. The fuel cell not only reduced the high impedance common to conventional fuel cells but the simple and relatively low temperature of operation allowed for low cost construction of the fuel cell using available materials and hardware.
This simple fuel cell can be built in much larger sizes than conventional fuel cells.
The conventional fuel cells, namely the proton electrolytic membrane fuel cell, the molten carbonate fuel cell, and the solid oxide fuel cell and their operating principles were described in PCT/AU97/00488 and will not be repeated in this patent application. The fuel cell covered in PCT/AU97/00488 is a major improvement over conventional fuel cells; however, there is further room for improvement as the electronic circuit had to pass through the electrolyte between the adjacent electrodes at the anode cell and again at the cathode cell. While this impedance may not be as great as conventional fuel cells, it was desirable to remove this impedance if possible and make the electronic circuit independent of the conductivity of the electrolyte. It would then be possible to use less corrosive electrolytes and also the possibility of using gases to conduct the ions between the anode cell and the cathode cell. This feature would also result in a higher fuel cell efficiency and higher power density.
It is the object or one of the objects of this invention to provide such an improved fuel cell.
In one form therefore the invention is said to reside in a fuel cell comprising a separate anode cell and a separate cathode cell, the anode cell including an anode tank for containing an electrolyte and having an anode electrode immersed therein, means to supply electrolyte to the anode tank and means to supply fuel to the anode tank, the cathode cell including a cathode tank for containing the electrolyte and having a cathode electrode immersed therein, means to supply electrolyte to the cathode tank and means to supply an oxidant to the cathode tank, means to withdraw reacted electrolyte from the anode tank and to supply it to the cathode tank, means to withdraw reacted electrolyte from the cathode tank and supply it to the anode tank, each of the anode electrode and the cathode electrode having a central current collector and a coating of catalyst thereon, each of the anode electrode and the cathode electrode having a first end and a second end, means to connect the first end of the anode electrode and the first end of the cathode electrode to a first electrical load outside of the fuel cell, and means to connect the second end of the anode electrode to the second end of the cathode electrode to a second electronic load as part of a complete electrical circuit of the fuel cell.
In one embodiment the second electrical load may comprise an ionic or semiconductor membrane or a diode device.
Each of the anode electrode and cathode electrode may have a composite cubical or cylindrical construction comprising an outer conductor current collector or collectors and a catalyst coating applied to its or their surfaces and an inner current collector electrically connected to the two outer conductor current collectors through an ionic or semiconductor membrane wherein the outer conductor current collector or collectors comprise the first end of the respective electrode and the inner current collector comprises the second end of the respective electrode.
To achieve the highest power output from the fuel cell the electrical loads may be connected to either the outer conductor current collector or collectors or the inner current collector depending on the specific ionic reactions occurring at each electrode.
Alternatively the respective inner current collectors may be connected directly together with the ionic or semiconductor membranes between the respective inner current collectors and outer conductor current collector or collectors providing the second electrical load.
In another embodiment the anode tank and the cathode tank may be separated by a common wall and the central collector of the anode electrode and the cathode electrode partially or completely connected through the common wall by an ionic or semiconductor membrane or a diode device providing the second electrical load.
In one preferred embodiment the means to supply electrolyte to the anode tank comprises the means to withdraw electrolyte from the cathode tank and the means to supply electrolyte to the cathode tank comprises the means to withdraw electrolyte from the anode tank.
There may be further included a reaction tank and wherein the respective means to supply electrolyte to the anode tank and to the cathode tank comprises means to withdraw electrolyte from the reaction tank and the respective means to withdraw reacted electrolyte from the anode tank and from the cathode tank transfers reacted electrolyte to the reaction tank.
There may be further included means for recovering excess fuel from the reacted electrolyte discharged from the anode cell and a means of removing reaction products from the anode tank, the cathode tank, or the reaction tank.
The anode tank and the cathode tank may be constructed to provide an efficient contact between the electrolyte containing the fuel or oxidant and the electrodes immersed in the electrolyte.
The anode electrode and the cathode electrode may be made from a material selected from the group comprising solid, porous, fibre, gauze, tiny particles of various shapes, or woven cloth of metal or alloys of metals, carbon, vitreous carbon, conducting plastics material or a slurry comprising fine particles comprising catalyst or coated with catalyst fluidised in the respective tanks.
The anode electrode and the cathode electrode may be electroplated, sputtered or coated with the catalyst selected from platinum, nickel, cobalt, lithium, lanthanum, strontium, palladium, rhodium, yttrium, or any mixtures of these.
The liquid electrolyte may be selected from the group comprising acidic electrolytes including sulphuric acid, phosphoric acid, methane sulphonic acid, other organic and inorganic acids, alkaline electrolytes including sodium hydroxide, potassium hydroxide, molten electrolytes including lithium-potassium carbonate, and mixtures of electrolyte and colloids or fine solid catalyst or fine particles coated with catalyst being a catalyst for the anode reaction and the cathode reaction.
Characteristics of the electrolyte may be altered by the addition of modifiers either as ions or colloids such as surfactants and metal ions such as vanadium oxide.
The electrolyte may be a gas selected from the group comprising nitrogen, helium, argon, or mixtures of these gases and other gases such as carbon oxides.
The fuel may be selected from the group comprising hydrogen, natural and refined hydrocarbons such as methane, propane, butane, liquid hydrocarbons, methanol, ethanol and other alcohols, and natural and manufactured carbohydrates such as biomass gas.
When the fuel is a hydrocarbon there may be further included means of cracking the hydrocarbon fuel or means of forming hydrogen from hydrocarbon fuels before introducing the fuel into the anode tank.
Where the fuel is a hydrocarbon there may be further included means to condition the hydrocarbon fuel prior to direct feeding to the fuel cell, the means to condition selected from pyrolysis with or without catalysis, contacting with a catalyst, contacting with a super acid or zeolite, or subjecting the hydrocarbon fuel to electromagnetic energy.
The oxidant may be selected from the group comprising air, oxygen, oxygen-nitrogen mixtures, oxygen-carbon oxide mixtures, hydrogen peroxide, and potassium permanganate.
There may be further included means for intermittent injection of gaseous fuel or oxidant respectively into the anode or cathode tanks.
Also there may be further included means to heat or cool the anode tank, or the cathode tank, or the reaction tank to a selected temperature and means to raise and maintain the pressure in the anode tank, or the cathode tank, or the reaction tank to a selected pressure.
In an alternative embodiment the invention may reside in a battery of fuel cells comprising a plurality of fuel cells as discussed above wherein the anode electrodes and the cathode electrodes of adjacent cells are electrically connected in series or in parallel.
In an alternative embodiment the invention may reside in a fuel cell having of a separate anode cell and a separate cathode cell and a reaction tank wherein: the anode cell comprises an anode tank having an anode electrode immersed therein, the anode electrode being selected from a monolithic electrode, a composite electrode, or an internally coupled electrode, means to supply electrolyte to the anode tank from the reaction vessel, means to supply fuel in the form of gas, liquid, or solid mixed with the electrolyte being supplied to the anode tank, the cathode cell comprises a cathode tank having a cathode electrode immersed therein, the cathode electrode being selected from a monolithic electrode, a composite electrode, or an internally coupled electrode, means to supply electrolyte to the cathode tank from the reaction tank, means to supply air, oxygen, oxygen-nitrogen mixtures, or other oxidants mixed with the electrolyte to the cathode tank, means to withdraw reacted electrolyte from the anode tank and deliver to the reaction tank, means to withdraw reacted electrolyte from the cathode tank and deliver to the reaction tank, each of the anode electrode and the cathode electrode having a first end and a second end, means to connect the first end of the anode electrode and the first end of the cathode electrode to a first electrical load outside of the fuel cell, and means to connect the second end of the anode electrode to the second end of the cathode electrode to a second electrical load as part of a complete electrical circuit of the fuel cell.
In an alternative embodiment the invention may reside in continuous process for producing electric power and heat in a fuel cell from reacting a fuel in an anode tank and an oxidant in a cathode tank, the fuel cell having an anode electrode immersed in the electrolyte in the anode tank, and a cathode electrode immersed in the electrolyte in the cathode tank and the anode electrode and the cathode electrode connected to a first electrical load at one end thereof and connected a second electrical load at another end thereof, the process comprising the steps of; introducing the fuel with the electrolyte in the anode tank wherein a catalyst on the anode electrode in the anode tank causes a chemical reaction or ionises the fuel thereby which producing electrons, transferring the electrons through an external electrical circuit through the external electrical loads to the cathode electrode, introducing the oxidant mixed with the electrolyte into the cathode tank wherein a catalyst on the cathode electrode causes a chemical reaction or ionises the oxidant with the electrons from the anode, and completing the electronic circuit.
The ions produced at the anode electrode required for the reaction at the cathode electrode may be delivered continuously through the electrolyte and the ions produced at the cathode electrode required for reactions at the anode electrode may be delivered continuously through the electrolyte.
This embodiment of the invention may further include a step of transferring the electrolyte from the anode tank and from the cathode tank to a reaction tank and transferring the electrolyte from the reaction tank to the anode tank and to the cathode tank and wherein the ions produced at the anode electrode and the ions produced at the electrode cathode are delivered continuously through the electrolyte to a reaction tank.
This embodiment of the invention may further include the step of recycling excess fuel exiting from the anode tank.
This embodiment of the invention may further include the step of removing the reaction products such as water or carbon dioxide from the electrolyte in an evaporating tank, vacuum vessel, or an absorption vessel.
This embodiment of the invention may further include a step of injecting gaseous fuel to the anode in a cyclic manner and injecting gaseous oxidant into the cathode tank in a cyclic manner.
The anode tank, the cathode tank, and the reaction tank may be heated or cooled and pressurised.
The oxidant, the electrolyte and the fuel may be as discussed above.
The fuel may travels co-current or counter-current to the electrolyte in the anode tank and the oxidant travels co-current or counter-current to the electrolyte in the cathode tank.
There may be several anode electrodes of the same type in one anode tank and correspondingly several cathode electrodes of the same type in one cathode tank. These electrodes may be electrically connected singly or in groups in series or in parallel. The optimum electrical connection of the electrodes depends on the catalyst and the electrolyte used but should naturally result in the highest voltage or power production from the fuel cell.
The electrode shape may be cubical, cylindrical, tube like or any geometrical shape and the electrodes may be installed along the flow or across the flow of the electrolyte.
In terms of electrolyte flow, several anode tanks may be connected singly or in groups in series or in parallel to a corresponding number of cathode tanks.
There may be further means to vary the ratio of the fuel and oxidant to the electrolyte fed into the anode tank and to the cathode tank and an additional means to add gas fuels in cyclic amounts to the anode tank.
The monolithic anode electrode and the monolithic cathode electrode may be made from materials selected from the group solid, porous, fibre, gauze, or woven cloth of metal, carbon, graphite, vitreous carbon, fine vitreous carbon beads, conducting plastics material, or a slurry comprising catalyst or fine particles coated with catalyst fluidised in the respective anode tank and cathode tank.
The composite anode electrode and the composite cathode electrode may be made from the same material as the monolithic electrode. The semiconductor or ionic membrane between the electrodes should allow the flow of electrons only in one direction and may be made from a range of materials such as plastics, ceramics, oxides and crystals.
The monolithic and the composite anode electrode and cathode electrode may be coated with catalyst by using with conductive binders or electroplating or by sputtering with catalyst selected from platinum, nickel, cobalt, lithium, lanthanum, strontium, palladium, yttrium, or any mixtures of these materials and their compounds.
The gaseous electrolyte may be selected from gases such as nitrogen, helium, argon, and compounds containing carbon and or hydrogen or oxygen.
The electrolyte may contain activators and modifiers as ions or fine particles or coatings of fine particles such as oxides of vanadium, potassium, and modifiers such as ionic and non-ionic surfactants to improve the efficiency of the fuel cell.
The ions produced at the anode required for the cathode reaction are delivered continuously by the electrolyte to the cathode tank.
The order of reactions may be true for a combination of catalyst and electrolyte but the reactions may vary with other combinations of catalyst and electrolyte.
For instance in a fuel cell using hydrogen for fuel and oxygen for oxidant and concentrated phosphoric acid for electrolyte, the reactions are:
Anode Reaction H2xe2x86x922H(+)+2e(xe2x88x92)
Cathode Reaction 1/2O2+2H(+)+2e(xe2x88x92)xe2x86x92H2O
The fuel cell reactions using hydrogen for fuel and oxygen for oxidant in a concentrated potassium hydroxide electrolyte are:
Anode Reaction H2+2OH(xe2x88x92)xe2x86x922H2O+2e(xe2x88x92)
Cathode Reaction 1/2O2+H2O+2e(xe2x88x92)xe2x86x922OH(xe2x88x92)
There may be further included the step of removing the fuel cell reaction products such as water and carbon dioxide from the reacted electrolyte in an evaporating vessel, a vacuum vessel, or an absorption vessel.
The process may be carried out in pressures from sub-atmospheric to 5,000 pounds per square inch and at temperatures from sub-zero temperatures to 1200xc2x0 C.
Heat produced from the fuel cell reaction may be may be recovered for co-generation, industrial heating, and domestic heating.
The fuel may travel co-current or counter-current to the electrolyte in the anode tank and the oxidant may travel co-current or counter-current to the electrolyte in the cathode tank.
Hence it will be seen that this invention is a chemico-electrical process to collect the electrical power and heat from the reaction of the fuel and oxidant. The process is carried out in a separate anode cell where fuel and electrolyte is introduced and a separate cathode cell where the oxidant and electrolyte is introduced. A complete electrical circuit is established between the anode electrode, the external electrical load, and the cathode electrode. Ion transport within the fuel cell is accomplished by circulating the liquid or gas electrolyte between the anode cell and the cathode cell.